Radio beacon shielding arrangement



Jan. 20, 1942. A. ALFORD RADIO BEACON SHIELDING ARRANGEMENT Filed Oct. 19, 1939 3 R m m; I uh M51 H m V. 1 A Y K 6 Z w w M 1 f 6 a m K M J 7/, m m T INVENTOR I'M DREW 14L FORD ATTORNEY Patented Jan. 20, 1942 UNITED STATES PATENT OFFICE RADIO BEACON SHIELDING ARRANGEMENT Application October 19, 1939, Serial No. 300,167

3 Claims.

My invention relates to radio guiding beacons and more particularly to improvements in radio guiding beacons for producing four indicating conditions for guiding airplanes along four courses.

Arrangements in the past have been constructed utilizing vertical antennae spaced at the corners of a square and energized alternately for the production of guiding beacons. However, such beacons suffer from the difficulty that vertically polarized energy is subject to a great many distortions, particularly due to reradiation from objects in the field of the transmitter. This difficulty is greatly increased as shorter wavelengths are used, since then many other objects which are insignificant in afiecting the waves at the lower frequencies become material in the field of the short wave radiations.

According to my invention I provide a beacon arrangement utilizing antennae designed for transmission of substantially purely horizontally polarized waves, thus avoiding distortions due to vertical objects in the field of radiation.

Furthermore, in the field of a radio beacon the objects quite near the transmitter tend to produce greater disturbances than those at a greater distance from the beacon due to the fact that the field near the beacon is much stronger and therefore stronger reradiations are produced.

In accordance with another feature of my invention I avoid largely the difficulties of distortions due to objects in the immediate field of the transmitter by providing a conductor shield or counterpoise spaced above the earths surface and arranged beneath the radiators of the beacon system.

Other objects and advantages of my invention will be apparent from a description of a preferred embodiment of my invention made in connection with the accompanying drawing, in which:

Fig. 1 illustrates a wiring diagram of the beacon system in accordance with my invention, and

Fig. 2 illustrates in perspective the structural arrangement of the beacon system and counterpoise in accordance with my invention.

Turning first to Fig. 1, HM, I02, I03 and I04, represent four antennae arranged at the corners of the square. Each of these antennae is made so as to produce substantially pure horizontal polarization of the radiated waves. Accordingly, I have illustrated each of these antennae as the type wherein each radiator comprises four radiating conductors I, 2, 3 and 4, the oppositely arranged conductors I and 3, and 2 and 4, being energized in phase opposition. The overall length of each of the conductors is made substantially equal to one-half of the operating wavelength measured from the center of the antennae unit to the ends of the inturned conductors. However, the radiating portion of these conductors are relatively short with respect to a wavelength of the energy produced so that a substantially uniform energization of the radiating portions of the conductors takes place.

By use of such antenna a substantially purely horizontally polarized wave is radiated. For a more complete description of the antenna structure reference may be had to my copending application Ser. No. 270,173, filed April 26, 1939.

The antennae IOI. I03 are interconnected by transmission line I01, a phase shift of being provided at I08, e. g. by a transposition. Transmission line I0! is connected by means of line I05 to terminal apparatus adjacent the transmitter I I0. These antennae are preferably spaced apart at their centers a distance substantially one-half the operating wavelength. When these antennae are connected to the source IIO, they are energized in phase opposition because of the transposition provided at I08. Consequently a radiation pattern substantially in the form of a figure 8 will be produced thereby.

Antennae I02, I04 are similarly connected over transmission lines I05. I09, to a point adjacent transmitter IIO These antennae are likewise spaced apart, preferably a distance equal to onehalf the operating wavelength so that they will form also a figure 8 pattern. The two figure 8 patterns overlap so that four guide lines are provided wherein the signals from two of the adjacent antennae will be equal, so that a course may be defined leading to the beacon transmitter. Antennae IOI, I03 and I02, I04 are alternately connected to transmitter source H0 by means of switch III operated in alternate fashion by keying means II2. This keying means may, if desired, produce the known type of interlocking signal commonly called the AN signals. Any other desired type of keying signal may be utilized preferably interlocking, however. Furthermore, instead of utilizing a switch III with a vibrator keying means, such as indicated at II2, any desired type of switch, such as a commutator switching arrangement or a rotatable cam system may be used.

In order that a spacing of a half-wave between centers may be achieved, it is clear that the antenna arrangement must have sides which are less than half a wavelength in length, otherwise it would not be possible to arrange four antennae independently energized in such a fashion.

It is, furthermore, well known that ordinary horizontal dipoles will not produce a purely horizontal polarization, but radiate fields having a vertical component, particularly in the directions near the ends of these radiators. Accordingly, with such dipoles the worst condition of vertical polarization fields occurs directly along the lines formed by the beacon. By utilizing antennae according to the design specifically described in my above-mentioned prior application, Ser. No. 270,173, this difficulty may be avoided since the antenna field according to the teachings of that application may be made to be less than half a wavelength on one side.

In the construction of radio beacons for guiding vehicles along a course, it has been found that distortions causing false or multiple courses occur primarily due to reflection or reradiation from objects in the field of the autennae and adjacent thereto. This harmful effect is considerably reduced by utilizing a radio beacon having substantially purely horizontally polarized waves as described above. However, in the immediate vicinity of the beacon, there are likely to be objects which may reradiate the horizontally polarized energy and thus produce errors in the guiding courses.

In order to avoid these harmful effects due to nearby conductors, I provide a beacon arrangement spaced at a vertical height above the earths surface and arranged beneath the antennae a metallic conductor sheet or counterpoise, as shown in Fig. 2. In this figure, four antennae forming the beacon are shown at Illl, I02, I03, and 684 arranged above a conductor sheet 2H]. In order to minimize trouble by radiation from the antennae feeding conductors, I prefer to use as feeders shielded conductor pairs. The shields for these conductors are preferably extended through conductor sheet 2H3 up to the antennae. Cross connections between the antennae are necessary in order that they may be energized. These connections are shown between antennae sea, H13 at 281, and between antennae I02, [04 at 2538. Between these cross connections and the antennae radiators is arranged conducting sheet or counterpoise 259. This sheet is preferably spaced from the earths surface a distance equal to a wavelength or more of the radiated energy and is preferably arranged a distance in the neighborhood of half a wavelength below the radiating antennae themselves. In a practical construction of this arrangement, the spacing of the antenna was made equal to \/26".

The arrangement of the cross conductors 201, 258 beneath the counterpoise prevents the radiated energy from the antennae from reaching these horizontal leads and being reradiated therefrom so as to cause interferences in the beacon pattern, and also serves as a shield for the leads 2| I, 212 connecting the antennae to the transmitter.

The counterpoise or conducting sheet 2!!! is not critical as to size, but should preferably be made sufiiciently large so as to provide a shield for the radiated energy at a substantial distance on all sides of the beacon radiators. Accordingly, the sheet should be as large as convenient construction permits and in any case should be greater than a wavelength in the direction of the antennae spacings. It is evident that the larger the shielding counterpoise the smaller will be the angle of radiation downwardly toward the earth and consequently the greater the distance at which the shield Will protect the beacon from influences of objects adjacent the transmitter.

I have shown one preferred embodiment of my invention wherein the radiating system comprises antennae designed for the transmission of substantially purely horizontally polarized waves. It

is clear, however, that the counterpoise arrangement in accordance with my invention may be usefully employed with other types of antennae, since it will provide a shield against radiation to nearby objects regardless of the type of polarization utilized. In all cases the shield should be sulficiently large so that it will not be resonant at the working frequency and produce interfering fields.

While I have described above a preferred embodiment of my invention, it should be understood that other adaptations thereof may be constructed without the departure from the spirit of my invention as defined in the accompanying claims.

What I claim is:

1. A four course radio beacon comprising two pairs of radiators, each radiator being designed to radiate substantially pure horizontally polarized waves, said radiators being arranged at the corners of a square the diagonal of which is substantially a half wavelength long at the operating frequency, shielded transmission lines connected respectively to diagonally arranged ones of said antennae, a source of radio frequency energy, means for alternately connecting said source to said respective transmission lines, to alternately energize said diagonally arranged antennae, whereby intersecting radiation patterns of horizontally polarized energy are produced and conductive means arranged beneath said radiator pairs and spaced from the surface of the earth.

2. A four course radio beacon comprising two pairs of radiators, each radiator being designed to radiate substantially pure horizontally polarized waves and comprising four radiating conductors arranged in the form of a square, each of said conductors being sent over at one end along the diagonal of said square, and connected together with diagonally arranged transposed conductors at their opposite ends, said radiators being arranged at the corners of a square the diagonal of which is substantially a half 7 wavelength long at the operating frequency, shielded transmission lines connected respectively to diagonally arranged ones of said antennae, a source of radio frequency energy, and means for alternately connecting said source to said respective transmission lines, to alternately energize said diagonally arranged antennae, whereby intersecting radiation patterns of horizontally polarized energy are produced.

3. A four course radio beacon comprising two pairs of radiators, each radiator being designed to radiate substantially pure horizontally polarized waves and each comprising four radiating conductors arranged in the form of a square, the radiating portion of each said conductor being less than a quarter of a wavelength long, each conductor having an overall length of substantially one-half a wavelength at the operating frequency, said radiators being arranged at the corners of a square the diagonal of which is substantially a half wavelength long at the operating frequency, shielded transmission lines connected respectively to diagonally arranged ones of said antennae, a source of radio frequency energy, and means for alternately connecting said source to said respective transmission lines, to alternately energize said diagonally arranged antennae, whereby intersecting radiation patterns of horizontally polarized energy are produced.

ANDREW ALFORD. 

